Variable resistor apparatus



July 11, 1950 a. F. TELLKAMP 2,514,682

VARIABLE RESISTOR APPARATUS Filed April 9, 1948 3 Sheets-Sheet 1 i z r July 11, 1950 a. F. TELLKAMP vmnsm RESISTOR APPARATUS 3 Sheets-Sfieet 2 Filed April 9, 1948 D [vi 012 0) 1 m QZZZZ,

1950 B. F. TELLKAMP 2,514,682

VARIABLE RESISTOR APPARATUS Filed April 9, 1948 3 Sheets-Shoat 3 Patenied duly ll, i950 2,514,682 VARIABLE RESISTOR APPARATUS Bernhard F. Tellkamp, Whitefish Bay, Wia, as signor to Allen-Bradley Company, Milwaukee, Win, a corporation of Wisconsin Application April 9, 1948, Serial his. 19.9%

it'll. 291-55) 6 Claims. i

This invention relates to variable resistance apparatus of the sliding contact type and resides more particularly in an improved form of the same in which parallel, concentric, circular reslstor and collector contact faces are electrically bridged by a sliding conductive brush, said brush having a resistor contacting portion of comparetively small area and an extended base which slidingly contacts the collector, the brush being independent of and transported by a carrier and urged by resilient means into electrical contact with the resistor and collector and at the same time into wedging engagement with the carrier to preclude backlash when direction of movement of the carrier is reversed.

An object of this invention is to provide a rheostat or potentiometer in which a brush in movable contact with a resistor element is free to maintain uniform and efiective electrical contact despite small dimensional inaccuracies in the faces contacted and which, at the same time, while preserving such contact is maintained against lost motion or backlash between itself and operating elements which cause its movement.

Another object of this invention is to provide a rheostat or potentiometer adapted to be constructed in compact form without sacrifice of uniform performance and long operating life.

This invention is herein described by reference to the accompanying drawings in which there is set forth by way of illustration and not of limitation specific forms in which apparatus may be constructed in accordance with thi invention.

In the drawings:

Fig. l is a front view in elevation with parts broken away and in section of one form of the apparatus of this invention;

Fig. 2 is a sectional view of the apparatus shown in Fig. l viewed through the plane 2-2;

Fig. 3 is a fragmentary sectional view of the apparatus shown in Fig. l viewed through the plane 3-3;

Fig. 4 is a detailed front view in elevation of the resistor and collector base member of the apparatus shown in Fig. i;

Fig. 5 is a perspective detail view of the brush carrier assembly of the apparatus shown in Fig. 1;

Fig. 6 is a perspective detail view of the brush maintaining spring of the apparatus shown in Fig. i;

Fig. '7 is a front detail view of the brush of the apparatus shown in Fig. 1;

Fig. 8 is a side view in elevation and in section of the brush shown in Fig. 7

Fig. 9 is a perspective view of the brush shown in Fig. l

Fig. 10 is a side view in elevation and in section of a compacted form of the apparatus of this invention;

Fig. 11 is a rear view in elevation and in section of the apparatus shown in Fig. 10 viewed through the plane H|I there indicated;

Fig. 12 is a front view in elevation and in section of the apparatus shown in Fig. 10 viewed through the plane |2|2 there indicated;

Fig. 13 is a top plan view in section of the carrier cap assembly of the apparatus shown in Fig. 10 viewed through the plane Iii-l3 indicated in Fig. 11; and

Fig. 14 is an enlarged detail perspective view of the brush employed in the apparatus illustrated in Fig. 10.

The embodiment of the invention illustrated in Figs. 1 to 9, inclusive, is in form suitable for use as a potentiometer of the type employed in communication and control circuits. In this form the apparatus is provided with an insulating base I preferably formed of molded synthetic resin. Incorporated in the base I as an integral part thereof is a resistor element 2 made up of a shallow layer of finely divided conductor particles for example carbon black dispersed and embedded as shown in the material composing the base i, for example as disclosed in Patent 2,269,136 issued to Bernhard F. Tellkamp, January 6, 1942. The resistance element 2 is circular in shape and interrupted by a gap 3. The ends of the resistor element 2 are electrically joined with metallic terminals 4 and 5 embedded in the material of the base i.

Surrounded by and concentrically disposed with respect to the resistor element 2 is a collector ring 6 also composed of a shallow layer of the base material 6 within which there is embedded and dispersed finely divided conductor particles. The nature and quantity of the con ductor particles making up the collector ring 6 is chosen to render the specific resistivity thereof low as compared with that of the resistor element 2 for example as disclosed in said Patent 2,269,136. The collector ring 5 is electrically joined with a side tap terminal 7 embedded in the material or the base i.

As more clearly appears in Figs. 2 and 3 the resistor element 2 and the collector ring 6 are depressed with respect to the forward face of the base I so as to occupy positions in the bottoms of circular grooves coincident therewith. In order to enhance insulation between the resistor ele- 3 ment 2 and the collector ring 6 the land between these elements is grooved as indicated at 8. By so extending the surface separating the resistor element 2 and the collector ring 6, coatings of conductive material resulting from wear are of less effect upon the maintenance of proper insulation.

Secured to the rear face of the base I is a mounting plate 9 which is rigidly attached in turn to a central bushing Ill. Mounted for rotation within the bushing i is an operating shaft l'l. Shaft II is provided with a groove occupied by a retaining ring l2 at the point where it emerges from the bushing Ill and with a reduced portion l3 at its opposite end. Between the shoulder formed by the reduced portion l3 and a retaining washer H at the end of the reduced portion l3 there is mounted and securely held in place a brush carrier I5 formed of insulating material.

The brush carrier l5 is of generally disc-shaped configuration with a projecting lug l6 extending from its periphery. Opposite the lug iii an axially disposed roughly triangular aperture l'l extends entirely through the disc of the carrier IS. The converging sides of the aperture ll form a reentrant dihedral angle which terminates at a flattened apex within the confines of the lug l6, providing surfaces for wedged engagement with a brush about to be described.

Disposed within the aperture i1 is a triangular brush I8 composed of electrically conductive carbon having carrier engaging surfaces is which converge on an angle complementary to the angle formed by the convergent surfaces of the aperture IT. The front face of the brush I8 is provided with a radially disposed inclined rib 20 more clearly depicted in Fig. 7, 8 and 9. The opposite face of the brush is provided with a resistor contacting foot 2i of limited area projecting laterally from a position adjacent the apex of the brush. Projecting laterally from the other two corners of the brush is a pair of collector ring feet 22--22 forming an extended base for contact with the collector ring 6.

The brush I8 is received within the recess I? as is more clearly shown in Figs. 1 and 2 and is maintained in position therein by the action of a circular spring 23. The spring 23 is anchored in position on the carrier [5 by notched engagement of a radial tongue 24 with a mortise 25 extendin through the disc of the carrier l5 as is more clearly shown in Fig. 2.

With the parts thus assembled the force exerted by the spring 23 against the inclined rib 20 causes the brush [8 to engage the resistor element 2 and the collector ring 6 with a 13-point engagement which will be maintained upon movement of the brush IS, in spite of irregularities in the surfaces contacted. This follows since the force of the spring 23 is applied within the triangular array formed by the contact feet 2| and 22-22. At the same time by reason of the inclined disposition of the rib 20 the force applied by the spring 23 includes a radial component causing the brush l8 to be urged outwardly into wedging engagement with the converging sides of the aperture II. In this way the brush I8 is positively held against angular displacement with respect to the carrier l5 even though the brush It may be displaced axially in accommodating to irregularities in the surfaces of the resistor element 2 and the collector ring 6.

Lug I 6 projecting from the rim of carrier l5 not only serves to accommodate the apex of the aperture ll but also acts in cooperation with parts 4 to be described as a means for limiting angular adjustment of the brush l8.

Enclosin and housing the electrical parts is a molded cap of insulating material 26 held in place by screws 21 which pass through the base I into threaded engagement with the mounting plate 9. The cap 26 is provided with an interior cylindrical recess of appropriate dimension to accommodate the parts to be housed and projecting inwardly radially from the walls of this recess is a stop 28 positioned as shown in Fig. 1. The stop 28 is so located as to be engaged by the lug it of the carrier l5 whenever the resistor contacting foot 2| approaches points near the ends of the resistor element 2.

While the apparatus as illustrated in Figs. 1 to 9, inclusive, is well adapted for mounting at the rear of a panel or wall of a cabinet for operation by a knob to be attached to the shaft i I, projecting through the panel or wall, it is sometimes desired that a rheostat or potentiometer be compacted and arranged for exterior mounting. The form of the apparatus of this invention illustrated in Figs. 10 to 14 is well adapted to compacting of the type referred to since the same includes, as shown, a brush carrier 29 which serves as well as a housing and a finger knob for actuation of the apparatus. The brush carrier 29 is formed of molded insulating material and is rigidly attached to a rotatable supporting shaft 3i by molding the same in place around the knurled head 30. Shaft 3! is mounted for rotation within a metallic collector terminal bushing 32 which is rigidly secured to a resistor base 33.

The resistor base 33 is composed of molded, insulating material including as an integral part thereof an interrupted circular resistor element 34 formed of embedded dispersed conductor particles, and a collector ring 35 of higher conductivity likewise formed of embedded dispersed conductor particles as above described. The base member 33 is roughly cylindrical in shape and includes a radially projecting lug 36 disposed opposite a gap 37 in the resistor element 343.

Brush carrier 29 includes a cylindrical recess 38 shaped to surround and house the base member 33. Projecting inwardly from the surface of the recess 38 is a stop 39 positioned to be engaged by the lug 36. Set into the floor (in of the recess 38 in the carrier 29 is a brush receiving aperture 4i having convergent walls 2 and 23 which terminate in an apex opposite the stop 39. The walls 42 and 23 are disposed in planes arranged parallel with the axis of the shaft 3! to permit free axial movement of a triangular brush id received therebetween.

Brush M is composed of conductive material, preferably carbon. and is provided with a resistor contacting foot 45 of limited area and collector ring contacting feet 46-d6. The brush M, as more clearly appears in Fig. 14, is provided with a radially inclined rear face 47 slopin upwardly toward the apex of the brush. Extending transversely with respect to the aperture 4| is a springaccommodating slot 48 within which a bowed wire spring 49 is received in position to resiliently act upon the sloping face 41 of the brush 44. Spring 49 thus may act to urge the brush 44 axially into contact with resistor element 34 and collector ring 35 and at the same time radially into wedged engagement with the converging surfaces 42 and 43 of the brush receiving aperture 4|. In this manner continuous electrical contact is at all times maintained and backlash 8 or lost movement between the brush it of the carrier 29 is precluded.

Collector ring 25 is disposed in electrical contacting relation to bushing 32 rendering the same effective for use as the electric terminal for the side tap contact of the apparatus. Embedded metallic terminals 50 and SI are molded in place within the base 33 in electrical contact with the ends of resistor element 34. with the apparatus constructed in the form illustrated in Figs. to 14, inclusive, the dimensions may be reduced to the point where the carrier 29 is of the minimum size which an operator's fingers may conveniently grasp and operate. There is thus provided an extremely compact construction and one in which the properties of consistent performance and long life are exhibited.

I claim:

1. In a variable resistance apparatus the combination comprising a base; an electrical resistor secured to said base having an exposed circular contact face; an electrically conductive collector secured to said base having an exposed circular contact face concentric with, electrically insulated from, and radially spaced with respect to said resistor contact face; a brush carrier mounted on said base for rotation with respect thereto about an axis concentric with said resistor and collector contact faces; said brush carrier including axially-extending, radially-convergent, brushengaging surfaces; a brush of conductive material having contacting portions spaced to span the spacing between said resistor contact face and said collector contact face disposed in electrical bridging contact relation thereto; said brush having axially-extending, radially-convergent. carrier-engaging surfaces of form complementary to the brush-engaging surfaces of said carrier, said complementary surfaces being in axially movable radially limited cooperative engagement with one another; and a spring mounted on said carrier in resilient pressure applying relation to said brush, adapted to act upon said brush to simultaneously urge the same axially into contact with said resistor and collector and radially into engagement with the radially-convergent, brush-engaging surfaces of said carrier; whereby said brush is subject to being revolved angularly with respect to and in maintained pressure contact with said resistor and collector contact surfaces upon rotation of said carrier without backlash between said carrier and brush.

2. In a variable resistance apparatus the combination comprising a base, an electrical resistor secured to said base having an exposed circular contact face; an electrically conductive collector secured to said base having an exposed circular contact face concentric with, electrically insulated from, and radially spaced from said resistor contact face; a brush carrier mounted on said base for rotation with respect thereto about an axis concentric with said resistor and collector contact faces; said brush carrier including a reentrant dihedral recess, the angular sides of which are formed of planes symmetrically disposed parallel to the axis of said carrier with the intersection of said planes located away from said axis; abrush of conductive material having contacting portions spaced to span the spacing between said resistor contact face and said collector contact face disposed in electrical bridging contact relation thereto said brush having external dihedral, carrier-engaging surfaces of form complementary to the reentrant dihedral surfaces of the recess in said carrier, said brush being contained in the recess in said carrier in axially movable radially limited cooperative engagement therewith; and a spring mounted on said carrier in resilient pressure applying relation to said brush, adapted to act upon said brush to simultaneously urge the same axially into contact with said resistor and collector and radially into engagement with the reentrant dihedral surfaces of the recess in said carrier; whereby said brush is subject to being revolved angularly with respect to and in maintained pressure contact with said resistor and collector contact surfaces upon rotation of said carrier without backlash between said carrier and brush.

3. A variable resistance apparatus in accord with claim 1 in which the contacting portions of said brush comprise a single resistor contacting portion and a pair of' separated collector contacting portions providing three points of engagement between the brush and the surfaces against which it is axially urged by the spring.

4. In a variable resistance apparatus including concentric circular resistor and collector elements mounted on an insulating base the combination therewith of a revolvable conductive bridging brush having a single resistor contacting foot in revolvable contact with said resistor element and a pair of collector contacting feet triangularly spaced therefrom in revolvable contact with said collector element, said brush having side surfaces converging toward an apex and an inclined back surface rising toward the apex of convergence of said side surfaces; a brush carrier mounted to rotate with respect to said base about an axis concentric with said resistor and collector elements, said carrier having a brush transporting recess therein including convergent walls disposed at an angle complementary to the angle of convergence of the side surfaces of said brush, said brush being disposed within said rccess in interfilling engagement therewith; and a spring secured to said carrier having a portion in resilient pressure applying engagement with the inclined back surface of said brush at a point within the triangle defined by said brush feet.

5. In a variable resistance apparatus the combination comprising an insulating base, an electrical resistor secured to said base having an exposed circular contact face interrupted by a gap; terminals secured to said base electrically joined to the ends of said resistor; an electrically conductive collector secured to said base having an exposed circular contact face substantially coplanar and concentric with, surrounded by and radially spaced from said resistor contact face; a terminal secured to said base and electrically Joined to said collector; a rotatable shaft; a brush carrier disc mounted on said shaft for rotation with respect to said base about an axis concentric with said resistor and collector contact faces and in facing relation thereto; said brush carrier disc including a triangular aperture therein having sides converging at a predetermined angle toward an apex remote from said shaft; a triangular brush of conductive material having a single resistor contacting foot projecting inwardly therefrom near an apex thereof and a pair of spaced collector contacting feet projecting inwardly therefrom near the ends of the brush sides emerging from said apex, the angle formed by said brush sides being substantially equal to said aperture angle; said brush being disposed in said aperture with said resistor contacting foot in contact with said resistor contact base and said collector contacting feet in contact with said collector contact face; and a spring mounted on said carrier disc in resilient pressure applying relation to said brush, adapted to act upon said brush to simultaneously urge the same axially into contact with said resistor and col- 7 exposed circular contact face substantially co planar and concentric with, surrounded by and radially spaced from said resistor contact face; a brush carrier actuating cap mounted on said base for rotation with respect thereto about an axis concentric with said resistor and collector contact faces and enclosing the same; said brush carrier cap including an inwardly facing dihedral recess having an apex which is remote from the axis of rotation of said cap and divergent sides which are perpendicular to the plane of rotation of said cap; a triangular brush of conductivemateria-l having a single inwardly projecting resistor contact foot opposite an apex thereof and a pair 30 2,383,987 of spaced collector contact feet projecting in-- 8 wardly therefrom near the ends of the brush sides emerging from said apex, the angle formed by said brush sides being substantially equal to the dihedral angle of said recess; said brush being disposed in said recess with said resistor contacting foot in contact with said resistor contact face and said collector contacting feet in contact with said collector contact face; and a spring mounted between said carrier cap and said brush, adapted to act upon said brush to simultaneously urge the same axially into contact with said resistor and collector elements and radially into engagement with the angular sides of said dihedral recess; whereby said brush is subject to being revolved angularly with respect to and in maintained pressure contact with said resistor and collector contact surfaces upon rotation of said carrier without backlash between said carrier and brush.

BERNHARD F. TE.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,997,427 Mucher Apr. 9, 1935 2,021,487 McDonell et a]. Nov. 19, 1935 2,346,598 Mucher Apr. 11, 1944 Penrose Sept. 4, 1945 

